Kim Kardashian May Have Been Left Off Sister Kendall Jenner's Birthday Bash List

— -- Trouble in Kardashian paradise?

Kendall Jenner celebrated her 19th birthday on Monday and apparently forgot to invite big sister Kim Kardashian, 34.

"We're going to go to a family lunch, and then later tonight Kendall's having like 15 people over for a little girls' party. I don't know if it's even a party, but a girls' gathering," Khloe Kardashian spilled to People magazine about the celebration.

But when the "Keeping Up With the Kardashians" star mentioned the party to Kim, she wasn't aware of anything.

"I asked Kim, 'Oh, are you going tonight?' and she was like, 'I didn't know Kendall was doing anything!'" Khloe added. "I don't know if she was late to be invited, but I'm invited, so I feel good about that!"

Khloe, 30, also gushed about how much Jenner has accomplished in just 19 years and that "I'm so proud of her, and she's still such a good girl."